1) Field of the Invention
The present invention relates to a library apparatus that automatically conveys a storage medium, such as a magnetic tape, to a recording and reproducing unit (a drive) to perform reading and writing of information or data from/in the storage medium, and more particularly, to a library apparatus that allows an operation to be performed without stopping the library apparatus, even in a state that a conveying mechanism is malfunctioning.
2) Description of the Related Art
In recent years, there has been an increasing demand for a library apparatus provided with magnetic tape cartridges for increase in data or information amount in a computer system or for retrieval of data requiring a mass storage, such as multi-media data or graphics data. The library apparatus has a function that automatically performs loading of each magnetic tape cartridge to a cell, unloading the same, storing the same, recording/reproducing data or the like.
Specifically, a magnetic tape library apparatus includes a medium handling robot (a conveying mechanism) called as “an accessor” for automating conveyance of each recording medium (each magnetic tape cartridge), with which insertion/ejection of the recording medium to/from a medium storage unit (a cell) or mounting and demounting to the cell and a recording and reproducing unit (MTU/drive) are automatically performed. The magnetic tape library apparatus is connected to a host computer for communication to automatically perform saving of a magnetic tape cartridge, recording/reproducing of data or the like according to an instruction from the host computer.
As explained above, a magnetic tape library apparatus of this type establishes a library system that conveys a magnetic tape cartridge to a predetermined position in a storage shelf and performs recording/reproducing in the recording/reproducing apparatus (see, for example, Japanese Patent Application Laid-open No. H7-174475, Japanese Patent Application Laid-open No. H7-44335, and Japanese Utility Model Application Laid-open No. 2003-515867).
In the conventional magnetic tape library apparatus, however, there is a problem described below. In the conventional magnetic tape library apparatus, since it is necessary to stop the magnetic tape library apparatus (shut off the power) to work during a maintenance thereof, or when a trouble occurs in a mechanical unit in the conveying mechanism provided in the magnetic tape library apparatus (at a time of failure), a system on the client side has to be down due to stopping of the library system itself.
Specifically, in a configuration where only one conveying mechanism is provided like the conventional magnetic tape library apparatus, when a trouble occurs in any of the mechanical units configuring the conveying mechanical apparatus, the magnetic tape library apparatus falls into malfunction as a whole. Consequently, there occurs a problem that the system on the client side is considerably affected by such a trouble.